1. Field of the Invention
The present invention relates to a current-sharing apparatus and a method thereof, and more particularly, to a current-sharing apparatus for automatically regulating the respective current-sharing amount and a method thereof.
2. Description of the Related Art
In general, the lifespan of an electronic element is significantly correlated to its operating temperature. The operating temperature also varies in direct proportion to a current flowing across the electronic element. For example, when an input voltage of a voltage regulator is very high, an output current and a voltage drop of the voltage regulator inevitably generate a certain amount of power consumption. Such power consumption increases the operating temperature of the voltage regulator.
The voltage regulator is commonly applied in the power management system of various electronic products for providing a regulated electrical power. FIG. 1 schematically shows a circuit diagram of a conventional voltage regulator. The voltage regulator comprises an unregulated DC input voltage VIN, a pass transistor 10, a regulated DC output voltage VO and a voltage divider composed of resistors 31 and 32. In addition, the voltage regulator further comprises a feedback control circuit electrically coupled to the pass transistor 10. Moreover, the feedback control circuit comprises an error amplifier 20 and a reference voltage VREF generated by a constant voltage generating unit 40. The feedback control circuit is electrically coupled to the DC output voltage VO via the voltage divider, and the resistors 31 and 32 are connected in series between the regulated DC output voltage VO and a ground reference. A joint of the resistors 31 and 32 is electrically coupled to a positive terminal of the error amplifier 20, and the reference voltage VREF is electrically coupled to a negative terminal of the error amplifier 20. In addition, an output terminal of the error amplifier 20 is electrically coupled to a gate of the pass transistor 10. Moreover, the feedback control circuit controls the impedance of the pass transistor 10 by modulating a gate voltage of the pass transistor 10. Currents with different levels are provided to an output terminal of the voltage regulator by the pass transistor 10 in response to the gate voltage of the pass transistor 10. Accordingly, a stable DC voltage is provided regardless the variances of the load condition and the input voltage of the voltage regulator.
A disadvantage of the conventional voltage regulator is that the operating temperature is too high when the input voltage is high. Another disadvantage of the conventional voltage regulator is that a voltage drop VD of the pass transistor 10 and the output current IO inevitably generate a power consumption PD. The power consumption PD causes an increment of the operating temperature of the voltage regulator. Since the operating temperature significantly impacts the lifespan of the voltage regulator, in order to improve its reliability, the operating temperature must be reduced as much as possible. Packaging process is also another factor to impact the operating temperature of the voltage regulator. It determines the thermo resistance and limits the thermo radiation. However, the packaging process with lower thermo resistance leads to a higher cost.